What else do I need to convert to EFI

71 Duster 318 4bbl
For an EFI system what do I absolutely need that I do not already have? What type of costs for what I do not have?
I have the MSD electronic ignition system
Fairly new fuel tank.
Edelbrock 1406 (4bbl) with a new aluminum intake manifold
I still have the old cast iron 2bbl intake manifold.